This text discusses synthetic membranes based on polyphenylene and modified polyphenylene oxide. It covers such membrane separation processes as low-pressure reverse osmosis, nanofiltration, membrane gas separation, membrane vapor separation, pervaporation and membrane battery separator as well as thin film composite membranes and novel membrane characterization methods. The contents of the book encompass almost all subjects that have to be considered in the design, preparation, performance testing and characterization of polymeric membranes. This text is aimed toward graduate students, research staff, professionals and government employees who conduct membrane R&D research, and engineers who design membranes and membrane modules as well as use membrane separation processes.